You can ask Scalefinishes.com if he has this kind of paint available or you can start looking for a Rustoleum or DupliColor alternative at a Home Depot type of store or an auto parts store like Pep Boys.

I was at hobby lobby this week and saw Krylon citrus green. Looks close to my eye but I'm not sure.

Can anyone confirm?

I just used the Krylon Citrus Green on a Porsche 911 model recently. I put it over grey primer and it was kind of dull, but after trying a white primer, pictures don't capture it, but I can say that it pops. I don't have a fire truck to compare it against but that was the first thing tht crossed my mind the first time I took it out into the sunlight. For $4 it would be worth trying.